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. 2020 Jan-Dec:19:1533033820980412.
doi: 10.1177/1533033820980412.

The Potential Role of Intensity-Modulated Proton Therapy in Hepatic Carcinoma in Mitigating the Risk of Dose De-Escalation

Luca Cozzi  1   2 , Tiziana Comito  1 , Mauro Loi  1 , Antonella Fogliata  1 , Ciro Franzese  1   2 , Davide Franceschini  1 , Elena Clerici  1 , Giacomo Reggiori  1 , Stefano Tomatis  1 , Marta Scorsetti  1   2
Affiliations

The Potential Role of Intensity-Modulated Proton Therapy in Hepatic Carcinoma in Mitigating the Risk of Dose De-Escalation

Luca Cozzi et al. Technol Cancer Res Treat. 2020 Jan-Dec.

Abstract

Purpose: To investigate the role of intensity-modulated proton therapy (IMPT) for hepatocellular carcinoma (HCC) patients to be treated with stereotactic body radiation therapy (SBRT) in a risk-adapted dose prescription regimen.

Methods: A cohort of 30 patients was retrospectively selected as "at-risk" of dose de-escalation due to the proximity of the target volumes to dose-limiting healthy structures. IMPT plans were compared to volumetric modulated arc therapy (VMAT) RapidArc (RA) plans. The maximum dose prescription foreseen was 75 Gy in 3 fractions. The dosimetric analysis was performed on several quantitative metrics on the target volumes and organs at risk to identify the relative improvement of IMPT over VMAT and to determine if IMPT could mitigate the need of dose reduction and quantify the consequent potential patient accrual rate for protons.

Results: IMPT and VMAT plans resulted in equivalent target dose distributions: both could ensure the required coverage for CTV and PTV. Systematic and significant improvements were observed with IMPT for all organs at risk and metrics. An average gain of 9.0 ± 11.6, 8.5 ± 7.7, 5.9 ± 7.1, 4.2 ± 6.4, 8.9 ± 7.1, 6.7 ± 7.5 Gy was found in the near-to-maximum doses for the ribs, chest wall, heart, duodenum, stomach and bowel bag respectively. Twenty patients violated one or more binding constraints with RA, while only 2 with IMPT. For all these patients, some dose de-intensification would have been required to respect the constraints. For photons, the maximum allowed dose ranged from 15.0 to 20.63 Gy per fraction while for the 2 proton cases it would have been 18.75 or 20.63 Gy.

Conclusion: The results of this in-silico planning study suggests that IMPT might result in advantages compared to photon-based VMAT for HCC patients to be treated with ablative SBRT. In particular, the dosimetric characteristics of protons may avoid the need for dose de-escalation in a risk-adapted prescription regimen for those patients with lesions located in proximity of dose-limiting healthy structures. Depending on the selection thresholds, the number of patients eligible for treatment at the full dose can be significantly increased with protons.

Keywords: RapidArc; VMAT; intensity-modulated proton therapy; liver cancer; stereotactic ablative radiation therapy.

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Conflict of interest statement

Declaration of Conflicting Interests: The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: L. Cozzi acts as Scientific Advisor to Varian Medical Systems and is Clinical Research Scientist at Humanitas Cancer Center. All other co-authors declare that they have no conflict interests.

Figures

Figure 1.
Figure 1.
The dose distribution in an axial plane for 3 patients failing in one or more constraints. In the first patient (left column), the constraints on the ribs were violated by both the RA and IMPT plans, the color wash set from 30 to 80 Gy. In the second case (right column) the RA plan violated the stomach maximum dose (color wash from 21 to 80 Gy) while in the third case (central column) RA violated the limits on the healthy liver sparing (color wash from 15 to 80 Gy).
Figure 2.
Figure 2.
The average dose-volume histograms for the CTV, the PTV and all the OARs accounted in the study.
See this image and copyright information in PMC

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